instead of making it work with a new ticket type...
|Reported by:||anonymous||Owned by:|
was checking your project a bit. I see where you are heading with it, and just wanted to throw out a thought. Instead of making it respond to a specific ticket type, and all the other custom fields you mentioned (start date, etc.)
You could consider one more additional field. A checkbox to include this ticket in the gantt-chart breakdown of a milestone. Doing so could automatically include the tickets blocking this one, if it is a master ticket. A condition could be that you have the required field estimated_hours or whatever the field name is for the timing and estimation plugin. even if you don't use that plugin, keeping the name of the field the same would help for consistency. Just a thought, doesn't seem like the right appication for a ticket type.